In liquid waste treatment processes, aeration introduces air into standing bodies of waste liquids (e.g., manure lagoons, waste ponds, water ponds and the like), adding fresh oxygen to the liquid and thereby providing an aerobic environment for microbial degradation of organic matter. More particularly, the purpose of this aeration is to supply the required oxygen to the metabolizing microorganisms and to provide mixing so that the microorganisms come into close contact with the dissolved and suspended organic matter, whereby to effect the desired microbial degradation.
Various aeration devices are currently available for aerating a liquid body. However, most commercially-available aeration devices add oxygen to the liquid body by means of propellers or rotors. This can create a problem in some situations, inasmuch as the propellers or rotors tend to generate substantial agitation in the liquid body.
More particularly, as described in the aforementioned U.S. Provisional Patent Application Ser. No. 60/578,767, filed Jun. 10, 2004 by William R. Campion for PRO-ACT MICROBIAL MANURE TREATMENT SYSTEM, in some circumstances the standing body of waste liquid may be subjected to a complex treatment system which “divides” the liquid into several different strata, each of which may undergo a different treatment regimen. By way of example but not limitation, in a manure pond, it may be desirable to provide a three strata treatment system: (i) a bottom anaerobic layer; (ii) an intermediate facultative layer; and (iii) a top aerobic layer. In such a system, it is generally desirable for the three layers to remain relatively segregated, and for only the top aerobic layer to be aerated. This may be further complicated inasmuch as in such a system, the top aerobic layer may be of variable thicknesses and, in some cases, may be relatively thin, e.g., only 6-12 inches thick.
As a result, using commercially-available propellers and rotors to effect aeration can present a problem, since the substantial agitation associated with propellers and rotors can cause the various layers of the liquid to mix. More particularly, while moderate intra-layer mixing of the liquid body may help the microorganisms to come into contact with the dissolved and suspended organic matter, intense inter-layer mixing of the liquid body is generally undesirable, since it disrupts the stratification of the liquid body, thereby making it more difficult to apply a separate treatment regimen to each layer of the liquid body. In addition, such intense inter-layer mixing of the liquid body is undesirable, since it adds oxygen to the lower facultative or anaerobic layers of the liquid.
In an effort to avoid the inter-layer mixing caused by the use of propellers and rotors, some systems replace the propellers and rotors with air diffusers placed on the floor of the lagoon. Unfortunately, while these air diffusers create less agitation than the aforementioned propellers and rotors, thereby minimizing undesirable inter-layer mixing, they also add oxygen to the lowest level in the lagoon, i.e., the anaerobic layer, which is precisely the layer which should not be oxygenated. Again, as noted above, adding oxygen to the anaerobic and facultative layers in the lower strata of the liquid body is generally undesirable. Furthermore, the oxygen from air diffusers placed on the floor of the lagoon only reaches the top target layer (i.e., the aerobic layer) after passing through the intervening anaerobic and facultative layers, which can reduce system effectiveness.